The invention disclosed herein relates to a continuously operating machine for inspecting vessels, especially plastic and glass bottles.
In beverage bottle plants, vessels that are contaminated, contain foreign bodies, or are damaged must be reliably detected and rejected prior to being filled with liquid. Numerous methods and apparatuses are known as in German-Offenlegungsschrift 30 36 502, German Patent 36 21 976, which permits a contactless, usually optoelectronic detection of contaminants, foreign bodies, and damage in or on bottles. Defects in returnable vessels of glass or plastic material which are used in the beverage industry cannot always be detected reliably by optoelectronic means and can only be detected with very expensive and complex methods. Some vessels may have fine hairline cracks or small holes in the bottom, side wall or mouth or areas so they cannot be refilled. This is true especially when the beverage is carbonated and the bottles are filled under counterpressure since the bottles are likely to leak and cause a slow decrease in the interior pressure as time goes on after the vessel filling operation. Defects in vessels may be caused by the thermal shock during a pre-inspection cleaning process or by force applied to the vessel during the filling operation which may be aggravated during each additional cleaning and filling cycle of a returnable bottle.
A machine described in U.S. Pat. No. 3,010,310 has been suggested for testing the resistance of glass bottles to pressure in order to detect defective bottles in a bottling line and in order to reject defective bottles. This high pressure testing machine is unsuitable for bottles or other containers having a thin wall consisting of a flexible or plastic material such as polyethylene terephthalate (PET). Moreover, a pressure test does not detect external damage to the bottle, if the defect is of a type that does not cause bottle leakage. A satisfactory system for detecting contaminants, dirt, foreign bodies, cleaning lye or liquid residues in empty bottles does not exist but is needed.